Among the transversal type lumber separators in use today, the apparatus which is the object of the heretofore quoted US patent is considered one of the most efficient performers in the industry, being known to reach piece counts up to 120 per minute, in its original mode of installation. Performance figures, however, have so far been largely influenced by two basic factors particular to the operating conditions, namely: a) the width and length variations of the pieces in the lumber supply, and b) the quality of material flow control in front of the separator. Inadequate regulation of the incoming lumber flow can produce opposite negative effects such as, on the one hand, lack of material at the loading point or, on the other hand, overlapping of pieces due to pressure build up in front of the separating device. It is well known in the industry that a flow of material consisting exclusively of 2".times.4" stock of uniform 8' length, does not present as many handling problems as does a production in dimensions from, for example, 1".times.4" to 2".times.10", in 8' to 16' mixed lengths, and that the capacity of any type of feed system may be greatly affected by the lumber dimension diversity factor.
In any event, and whatever might be the limitations of present day feed systems, production advances in sawmilling have made it necessary to raise the piece count for lumber separators from a ceiling of some 120 pieces per minute, under best conditions, to numbers above 180 per minute; in other words, an increase of some 50% in operating potential is required. This need for extra piece handling capacity stems not only from the process of industrial integration which has caused individual mills to grow in size, but also from a forest resource conservation principle which dictates that more lumber should be produced from the small logs available, including the usable portion of tree tops. While this procedure results in larger production volumes, it also causes a disproportionate increase in the number of pieces to be handled through the various manufacturing stages.
Beyond the need for ever shorter loading/offloading cycles in lumber feeding devices, a further condition is imposed on these systems as a result of present high conversion rate policies which have now firmly established such processes as curved sawing (producing bowed pieces) and marginal edging (causing imperfect squaring off) as basic rules of production. As a consequence, the overall production volume in a modem sawmill contains an important proportion of rough sawn pieces having shape irregularities to be corrected in the final processes of length trimming and kiln stacking. The industry is therefore faced with an urgent need for performance improvements in feeding systems to all processes, more particularly the final ones, where the total mill production is to be separated into a succession of individual pieces for trimming, sorting and stacking.